1. Field of the Invention
The present invention relates to an organic electroluminescent device that can provide an improved image quality and have price competitiveness, and a fabrication method thereof.
2. Description of the Related Art
Generally, organic electroluminescent devices (OELD) emit light using energy released from exited electrons when the excitons transit from an excited state to a ground state after generating the excitons by injecting electros and holes from a cathode and an anode.
Since the organic electroluminescent device (OELD) emits light by itself, a separate light source is not required in the OELD, while a liquid crystal display device (LCD) requires a separate light source such as a backlight unit. Therefore a volume and a weight of a display device can be reduced using the organic electroluminescent device.
The organic electroluminescent device (OELD), furthermore, has high-quality panel characteristics such as low-power consumption, high-luminance, rapid response time, and being light-weight. Due to such high-quality panel characteristics, the OELD has been spotlighted as a next generation of a display device, which may be applied into consumer electronic devices such as a mobile communication terminal, a CHS, a PDA, a camcorder and a Palm PC.
Such an OELD may be manufactured through a simple fabricating method compared to other flat display devices. Accordingly, the manufacturing cost of the OELD may be significantly low compared to a conventional LCD device.
A driving mode of the OELD is classified into a passive matrix type and an active matrix type.
The passive matrix type OELD has a simple structure, and a fabrication method thereof is also simple. However, the passive matrix type OELD has disadvantages such as high power consumption, difficulty in embodying a large-screen OELD and a dropping of an opening-ratio in proportional to the number of lines.
The active matrix type OELD provides a high emitting ratio and a high-image quality.
FIG. 1 shows an organic electroluminescent device (OELD) according to a related art.
Referring to FIG. 1, the organic electroluminescent device (OELD) 10 includes a thin film transistor (TFT) array 14 formed on a first transparent substrate 12, a first electrode 16 formed on the TFT array 14, an organic light emitting layer 18 and a second electrode 20.
The light emitting layer 18 expresses red, green and blue colors. Such a light emitting layer 18 is generally formed by depositing organic materials emitting the red, green and blue colors at each of pixels P and patterning the organic materials.
The organic electroluminescent device 10 is fabricated in a capsulated shape by adhering the first substrate 12 to a second substrate 28 having a moisture absorption 22 through a sealant 26.
The moisture absorption 22 is for removing moisture and oxygen which may penetrate into the capsulated electroluminescent device 10. In order to form the moisture absorption 22 on the second substrate 28, a predetermined region of the substrate 28 is etched, the etched region is filled with the moisture absorption 22 and the moisture absorption 22 is fixed using a tape 25.
Hereinafter, a TFT array that is a pixel in an OELD according to a related art will be described with reference to FIG. 2.
FIG. 2 is a plan view showing a thin film transistor (TFT) array in an organic electroluminescent device (OELD) according to a related art.
An active matrix type TFT array includes a plurality of pixels defined on a substrate 12. Each of the pixels includes a switching thin film transistor (TFT) TS, a driving thin film transistor (TFT) TD and a storage capacitor CST. Each of the switching TFT TS and the driving TFT TD may be configured of one or more thin film transistors according to the driving characteristics.
The substrate 12 may be a transparent insulating substrate made of glass or plastic.
As shown in FIG. 2, a gate line 32 is arranged on the substrate 12 in one direction and a data line 34 is arranged to cross the gate line 32 with an insulating layer interposed.
At the same time, a power line 35 is formed to be separated from the data line 34 at a predetermine distance in parallel.
Thin film transistors configured of gate electrodes 36 and 38, active layers 40 and 42, source electrodes 46 and 48 and drain electrodes 50 and 52 are used as the switching TFT TS and the driving TFT TP.
As described above, the gate electrode 36 of the switching TFT TS is connected to the gate line 32, and the source electrode 46 is connected to the data line 34.
The drain electrode 50 of the switching TFT TS is connected to the gate electrode 38 of the driving TFT TD through a contact hole 54.
The source electrode 48 of the driving TFT TD is connected to the power line 36 through a contact hole 56.
The drain electrode 52 of the driving TFT TD is formed to contact the first electrode 16 formed at the pixel region P.
The power line 35 and the first electrode 16 which is a poly-crystal silicon layer formed under the power line 35 form the storage capacitor CST by being overlapped with one another with the insulating layer interposed therebetween.
Hereinafter, a pixel arrangement of the related art organic electroluminescent device (OELD) will be described with reference to FIGS. 3A to 3C.
FIGS. 3A to 3C show arrangements of sub pixels in an organic electroluminescent device according to a related art.
Referring to FIGS. 3A to 3C, red, green and blue sub pixels are arranged based on a RGB stripe mode, a RGB mosaic mode and a RGB delta mode, respectively.
In the RGB strip mode as shown in FIG. 3A, the red, green and blue sub pixels of a pixel P are arranged in sequence at each of lines. In the RGB mosaic mode as shown in FIG. 3B, the red, green and blue sub pixels of a pixel P are arranged in sequence at a first line, and the green, the blue and red sub pixels of another pixel are arranged in sequence at a second line. At the third line, the blue, the red and green sub pixels of another pixel are arranged in sequence. In the R G B delta mode as shown in FIG. 3C, the red, green and blue sub pixels of a pixel P are arranged in sequence at each of the lines with the sub pixels of a pixel P arranged at even lines deviated from those of another pixel arranged at odd lines at a predetermined distance.
Each of the red, green and blue sub pixels in each pixel in the related art OELD is formed to have a vertical side longer than a horizontal side. Also each pixel in the related art OELD is formed by arranging the red, green and blue sub pixels in the horizontal direction, and the related OELD is formed by repeatedly arranging such pixels.
However, general visual information includes lots of horizontal movement compared to vertical movement. Therefore, the conventional arrangement of sub pixels cannot display images naturally.
In order to naturally display visual information having lots of horizontal movement through the conventional OELD, a resolution thereof must be increased.